Comparison of Health-beneficial Secondary Metabolites in Red Raspberry Grown under Field and High Tunnel Production Systems

High tunnels offer numerous benefits and have been adopted for wide usage in raspberry production in the United States, primarily with fall-fruiting primocane cultivars.  Use of high tunnels extends the harvest season, increases yields, and improves overall fruit quality with minimal economic inputs.  Marketable yields are also significantly increased with fewer pesticide inputs because fruit is protected from moisture, frost, and wind.  The effect of  high tunnel production on the production of plant secondary metabolites is less well defined.  In this study, anthocyanins, ellagitannins, and carotenoids were measured using high performance liquid chromatography (HPLC) for three fall-fruiting red raspberry cultivars (‘Autumn Britten’, ‘Caroline’, and ‘Nantahala’) grown at three locations in North Carolina in field and under high tunnel cultivation. At 520 nm, HPLC detected either four or eight anthocyanins (measured as mg/g cyanidin-3-glucoside equivalents), depending on cultivar.  Eight anthocyanins each were detected in ‘Autumn Britten’ and ‘Caroline’, and four anthocyanins in‘Nantahala’.  Using HPLC wavelength at 280 nm, two phenolic acids (measured as mg/g ellagic acid equivalents), specifically ellagitannins, were identified in all three cultivars.  Using ANOVA, the primary contributing factor to variation in anthocyanin concentration was cultivar, with no significant differences in content found for most of or the majority of detected anthocyanin and phenolic acid compounds between field and tunnel grown fruit samples.  The exception was cyanidin-3-glucoside, where samples grown under field cultivation (4.061 mg/g) had significantly higher (P = 0.008) levels than those grown under tunnel cultivation (3.440 mg/g).  This is consistent with our related research, where cyanidin-3-glucoside levels  increased as exposure to temperatures over 29 °C increased during the harvest period.  Our results suggest that the sheltered environment of the tunnel has a cooling effect on the fruit, which may in turn affect the accumulation of cyanidin-3-glucoside.  Additionally, the carotenoid profile was determined for these berries and production components.  Only cultivar significantly affected values, with ‘Nantahala’ having less beta and alpha carotene than ‘Autumn Britten’ or ‘Caroline’.  Our findings show that germplasm had the strongest effects on the type and content of secondary metabolites in raspberry fruit.